In a nutshell, their brains evolved differently than other species of birds so as to acquire the high intelligence and speaking ability (*). PLUS, the genes involved in brain development -which is what evolved differently in parrots- are the same human genes that have to do with stuff like autism, developmental disabilities and schizophrenia! How super cool is that?!
https://indianapublicmedia.org/amomento ... lutionary/
* And, another thing that makes them different is that, in birds, the more precocial the species is (a precocial species is one that the baby resembles and can do almost the same things as an adult can -like ducklings that come out of the egg with feathers, walking, eating and swiming on their own), the more protein the egg has BUT parrots eggs have as much or more protein than super precocial species even though they are very altricial (altricial are species that the baby depends entirely on their parents because it's born without feathers, with eyes closed, not being able to feed on its own, etc)- why? Because they need the extra protein to grow that big brain of theirs!




